fix(docs): add comma following _scheme value (#189)

Author: erikreyna

docs/schemes/oauth2.md

@@ -10,7 +10,7 @@
 auth: {
   strategies: {
     social: {
-      _scheme: 'oauth2'
+      _scheme: 'oauth2',
       authorization_endpoint: 'https://accounts.google.com/o/oauth2/auth',
       userinfo_endpoint: 'https://www.googleapis.com/oauth2/v3/userinfo',
       scope: ['openid', 'profile', 'email'],